1. Field of the Invention
The present invention relates to an electrical contact of an electric component to be mounted to a printed circuit board, such as electrical connector, carrier chip switch, capacitor, electrical connection member or any other electrical part, and more particularly to an improved shape of the soldering portion of an electrical contact of such surface-mounted component.
2. Description of the Prior Art
As is well known, a variety of electric components are mounted to a printed circuit board by soldering the lead wire terminals of such electrical components to the surface of the printed circuit or by connecting them to the surface of the printed circuit with the aid of lead-less means. In the former the strength with which the lead wire terminals are fixed to the surface of the printed circuit, and the quality with which the lead wire terminals are electrically connected to the surface of the printed circuit depends on the shape of the lead wire terminal, and on the soldering condition resulting from the particular shape of the lead wire terminal. Therefore, the lead wire terminal shape and the soldering strength attained thereby have been studied, and these factors are taken into consideration in designing lead wire terminals.
A conventional lead wire terminal is shown in FIG. 8. As shown, the soldering portion 2' of the terminal 1' is of rod shape. The end surface 3' of the rod-shaped soldering portion 2' is put on a conductor, and then its surface is joined to the surface of the conductor as indicated at 4'. As shown, the soldering skirts the lead wire terminal.
Advantageously, the rod-shape of this lead wire terminal soldering portion 2' makes it easy to produce a lot of such metal pieces by stamping metal sheets. When an exterior force is applied to the terminal 1', the soldering skirt 4' will be loaded from the soldering portion 2'. Disadvantageously, the load per unit soldering area will be great because of the relatively small contact area between the rod-shaped soldering portion 2' and the surrounding soldering skirt 4', and therefore, the soldering portion 2' is liable to be removed from the conductor.
FIG. 9 shows another conventional lead wire terminal 11' having an "L"-shaped soldering portion 12'. It is composed of a horizontal foot 13'. As shown, the end surface 14' of the foot 13' of the "L"-shaped soldering portion 12' is put on the conductor, and then the surface of the soldering portion 12' is joined to the surface of the conductor as indicated at 15'.
When an undesired exterior force is applied to the lead wire terminal 11', the load per unit area on the soldering skirt 15' will be relatively small because the end surface area 14' is relatively large, accordingly increasing the resistance of the soldering portion against the exterior force to remove the lead wire terminal 11' from the underlaying conductor. In case that a strong pull is applied to the vertical leg 16' of the lead wire terminal 11', the pulling force is liable to concentrate to the bent portion "P" of the "L"-shaped soldering portion 12 . As a result a fatigue failure is liable to appear at this bent portion, allowing the soldering portion to be removed from the conductor. The jointing strength between the soldering and the conductor results only from the soldering around the bent portion of the "L"-shaped lead wire terminal. The remaining contact area of the "L"-shaped piece even though it is relatively large in area, has little effect of increasing the jointing strength.
With the above in mind, the object of the present invention is to provide a surface-mounted component's contact having an improved soldering portion which is capable of preventing localized concentration of force in the soldering portion as is the case with a conventional "L"-shaped contact when pulled up, and is capable of minimizing the load per unit soldering area upon application of undesired external force to the contact, thereby preventing the fatigue failure or removal of the contact from the conductor, and assuring that sufficient joining strength to the conductor is maintained at all times and that good electrical contact is kept at all times.
To attain this object a surface-mounted component's contact having a soldering portion, which contact is to be mounted to the surface of a printed circuit board and is to be electrically connected to a conductor on said printed circuit board by soldering its soldering portion to said conductor, is improved according to the present invention in that said soldering portion comprises a fat foot and a leg, which is integrally connected to and rising from the midportion of said foot, thus generally shaped in the form of an inverted "T", said soldering portion being a metal piece made by stamping a metal blank.
The soldering portion of the contact has an extensive foot, and the soldering material will be applied over this extensive foot. When an undesired external force is applied to the contact, and hence the soldering skirt, the force will be distributed evenly over the extensive area of the contact foot, thus reducing the load per unit soldering area to possible minimum.
In case that a strong pull is applied to the contact to raise it apart from the conductor, the force will be transmitted to the horizontal foot via the joint between the horizontal foot and the vertical leg of the contact, and will be evenly distributed in the surrounding soldering skirt in all directions thanks to the location of the joint in the midpoint of the foot. Thus, no fatigue failure will be caused in the soldering skirt, and the peeling-off of soldering material will be prevented. The inverted "T"-shape of the contact piece has the effect of holding the joint strength and electrical contact in good, reliable condition.
The inverted "T"-shape of the contact piece permits the stamping-out of the contact from metal sheets. This assures that a metal piece has a strong joint between horizontal and vertical portions.